HERAT, Afghanistan (AFP) — Police in Afghanistan said Wednesday that clashes and US-led air strikes against insurgents had killed 100 people, most of them civilians, in one of the deadliest battles in nearly eight years.

The US military opened an investigation into the operation overnight Monday into Tuesday in the remote western province of Farah, as Afghan President Hamid Karzai ordered his government to probe reports of high civilian casualties.

"During the aerial bombardment and ground operations, more than 100 people have died," western Afghanistan police spokesman Abdul Rauf Ahmadi told AFP, basing his information on reports from police, the Red Cross and locals.